There are a variety of applications, such as food packaging, that require packaging film that have excellent tensile, heat seal and gas barrier properties. However, there are several problems with current packaging films.
U.S. Pat. No. 4,643,945 (Kiang) discloses a polymer blend useful for forming heat sealable plastic film, which comprises 60% to 40% by weight of propylene-ethylene-butene terpolymers wherein the ethylene content is about 0.1-10.0 mole percent and the 1-butene content is about 0.1-10.0 mole percent, and about 40%-60% by weight of a second component of copolymers of ethylene and alpha olefins containing four or more carbon atoms. The examples indicate seal initiation temperatures in the range of 105° C. to 120° C. These seal initiation temperatures are generally considered to be high.
U.S. Pat. No. 5,530,065 (Farley) discloses a film comprising at least one layer containing from of about 40 to of about 99 weight percent of a metallocene polyethylene copolymer and about 1 to 60 weight percent on a Ziegler-Natta based ethylene interpolymer such as linear low density polypropylene (LLDPE). These blends have low seal initiation temperatures. However, it is difficult to process these polymers in the conventional sequential machine direction orientation (MDO) and transverse direction orientation (TDO) biaxially oriented polypropylene (BOPP) process due to the very low melting temperatures associated with these polymers.
U.S. Pat. No. 5,874,139 (Bosiers) discloses a multi-layer structure having a sealant layer and a polypropylene layer, the sealant layer comprising a polymer mixture of from about 30 to 55 weight percent of a homogeneously branched substantially linear ethylene copolymer having a density in the range of 0.885 and 0.905 g/cc and 45 to 70 weight percent of a heterogeneously branched linear ethylene copolymer with a density in the range of 0.91 to 0.95 g/cc. The heat seal initiation temperature of these resin blends is in the range of existing BOPP films. However, Bosiers' polymers suffer from the same defects as Farley's polymers.
U.S. Pat. No. 5,888,648 (Donovan) discloses a multilayer film for forming hermetic seals comprising a main film substrate and a two-layer sealant layer which itself comprises of an intermediate layer selected for sufficient flow property under sealing conditions and an outer sealant layer bonded to the intermediate layer to provide a seal under sealing conditions. Resins cited in the examples for the intermediate layer are LLDPE, ethylene-propylene random copolymer, ethylene-propylene-butene terpolymer, a metallocene catalyzed polyethylene, and blends of these. The sealant layer resins cited in the examples are ethylene-propylene-butene terpolymers or ethylene-propylene random copolymer. Such film structures are expensive and bulky due to the thick intermediate layer required to achieve a hermetic seal.
U.S. Pat. No. 6,190,760 (Nagai) discloses an oriented metallized polypropylene film comprising a metal adhesion layer of a polypropylene resin of mesopentad fraction 60-88%. A coextruded heat sealable layer opposite the metal adhesion layer comprises an ethylene-propylene-butene terpolymer. This film does not have good low seal initiation properties.
U.S. Pat. No. 6,231,975 (Kong) discloses an oriented sealable film comprising an inner layer comprising greater than 80% by weight of isotactic polypropylene or syndiotactic polypropylene, a sealing layer which can be an ethylene-propylene random copolymer, ethylene-butene copolymer, ethylene-propylene-butene terpolymer, butene-propylene copolymer, Ziegler Natta catalyzed polyethylene or a metallocene catalyzed polyethylene, and a separable layer positioned between the inner layer and sealing layer. The separable layer comprises a blend of linear low density polyethylene and ethylene-propylene block copolymer. Kong's film would not have the proper seal initiation properties without the separable layer.
U.S. Pat. No. 6,423,420 (Brant) discloses an oriented multilayer film, comprising an outer layer comprising a metallocene catalyzed polyethylene having a density of 0.900 to 0.935 g/cm3 and a composition distribution breadth index of 50 to 95%; and a polypropylene core layer. This film does not have good low seal initiation temperature properties.
U.S. Pat. No. 6,458,469 (DeLisio) discloses an oriented multilayer film comprising a base layer, at least one tie layer, and at least one outer layer consisting of a metallocene catalyzed polyethylene. This metallocene catalyzed polyethylene layer does not have good low seal initiation temperature or hot tack properties.
U.S. patent application Ser. No. 10/744,081 (Su) discloses blends of propylene-ethylene-butene terpolymer and metallocene-catalyzed polyethylene or metallocene-catalyzed ethylene copolymers. This film does not have good low seal initiation properties.
In light of the deficiencies of the prior art, this invention provides several advantages, among others, to provide an economical solution to the product packager and provide the heat seal properties of a low seal initiation temperature, hot tack performance, high hermetic seal attributes and seal through contamination as well as superior flat sheet and formed bag barrier durability.